The role of cyclic nucleotides in tranmission through sympathetic ganglia will be studied. It is known that catecholamines and related amines increase the ganglionic content of cAMP and that muscarinic cholinomimetic drugs increase the ganglionic content of cGMP. The relationships between these drug-induced changes in cyclic nucleotides and their effects on transmission will be studied. Studies to date show that marked differences exist between dose-response curves that describe the blockade of transmission by catecholamines and the ability of catecholamines to stimulate adenyl cyclase. Electrophysiological studies show that the catecholamines cause ganglionic hyperpolarization but do not change input membrane resistance. These results suggest an electrogenic mechanism related to metabolism rather than passive changes in permeability.